diff --git a/src/__tests__/billing.test.ts b/src/__tests__/billing.test.ts
new file mode 100644
index 0000000..07790dc
--- /dev/null
+++ b/src/__tests__/billing.test.ts
@@ -0,0 +1,294 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import express from "express";
+import request from "supertest";
+
+// We need to mock Stripe before importing billing router
+vi.mock("stripe", () => {
+  const mockStripe = {
+    checkout: {
+      sessions: {
+        create: vi.fn(),
+        retrieve: vi.fn(),
+      },
+    },
+    webhooks: {
+      constructEvent: vi.fn(),
+    },
+    products: {
+      search: vi.fn(),
+      create: vi.fn(),
+    },
+    prices: {
+      list: vi.fn(),
+      create: vi.fn(),
+    },
+    subscriptions: {
+      retrieve: vi.fn(),
+    },
+  };
+  return { default: vi.fn(() => mockStripe), __mockStripe: mockStripe };
+});
+
+let app: express.Express;
+let mockStripe: any;
+
+beforeEach(async () => {
+  vi.clearAllMocks();
+  vi.resetModules();
+
+  process.env.STRIPE_SECRET_KEY = "sk_test_fake";
+  process.env.STRIPE_WEBHOOK_SECRET = "whsec_test_fake";
+
+  // Re-import to get fresh mocks
+  const stripeMod = await import("stripe");
+  mockStripe = (stripeMod as any).__mockStripe;
+
+  // Default: product search returns existing product+price
+  mockStripe.products.search.mockResolvedValue({ data: [{ id: "prod_TygeG8tQPtEAdE" }] });
+  mockStripe.prices.list.mockResolvedValue({ data: [{ id: "price_123" }] });
+
+  const { createProKey, findKeyByCustomerId, downgradeByCustomer, updateEmailByCustomer } = await import("../services/keys.js");
+  vi.mocked(createProKey).mockResolvedValue({ key: "pro-key-123", tier: "pro", email: "test@test.com", createdAt: new Date().toISOString() } as any);
+  vi.mocked(findKeyByCustomerId).mockResolvedValue(null);
+  vi.mocked(downgradeByCustomer).mockResolvedValue(undefined as any);
+  vi.mocked(updateEmailByCustomer).mockResolvedValue(true as any);
+
+  const { billingRouter } = await import("../routes/billing.js");
+  app = express();
+  // Webhook needs raw body
+  app.use("/v1/billing/webhook", express.raw({ type: "application/json" }));
+  app.use(express.json());
+  app.use("/v1/billing", billingRouter);
+});
+
+describe("POST /v1/billing/checkout", () => {
+  it("returns url on success", async () => {
+    mockStripe.checkout.sessions.create.mockResolvedValue({ id: "cs_123", url: "https://checkout.stripe.com/pay/cs_123" });
+    const res = await request(app).post("/v1/billing/checkout").send({});
+    expect(res.status).toBe(200);
+    expect(res.body.url).toBe("https://checkout.stripe.com/pay/cs_123");
+  });
+
+  it("returns 413 for body too large", async () => {
+    // The route checks content-length header; send a large body to trigger it
+    const largeBody = JSON.stringify({ padding: "x".repeat(2000) });
+    const res = await request(app)
+      .post("/v1/billing/checkout")
+      .set("content-type", "application/json")
+      .send(largeBody);
+    expect(res.status).toBe(413);
+  });
+
+  it("returns 500 on Stripe error", async () => {
+    mockStripe.checkout.sessions.create.mockRejectedValue(new Error("Stripe down"));
+    const res = await request(app).post("/v1/billing/checkout").send({});
+    expect(res.status).toBe(500);
+    expect(res.body.error).toMatch(/Failed to create checkout session/);
+  });
+});
+
+describe("GET /v1/billing/success", () => {
+  it("returns 400 for missing session_id", async () => {
+    const res = await request(app).get("/v1/billing/success");
+    expect(res.status).toBe(400);
+  });
+
+  it("returns 409 for duplicate session", async () => {
+    // First call succeeds
+    mockStripe.checkout.sessions.retrieve.mockResolvedValue({
+      id: "cs_dup",
+      customer: "cus_123",
+      customer_details: { email: "test@test.com" },
+    });
+    await request(app).get("/v1/billing/success?session_id=cs_dup");
+    // Second call with same session
+    const res = await request(app).get("/v1/billing/success?session_id=cs_dup");
+    expect(res.status).toBe(409);
+  });
+
+  it("returns existing key page when key already in DB", async () => {
+    const { findKeyByCustomerId } = await import("../services/keys.js");
+    vi.mocked(findKeyByCustomerId).mockResolvedValue({ key: "existing-key", tier: "pro" } as any);
+    mockStripe.checkout.sessions.retrieve.mockResolvedValue({
+      id: "cs_existing",
+      customer: "cus_existing",
+      customer_details: { email: "test@test.com" },
+    });
+    const res = await request(app).get("/v1/billing/success?session_id=cs_existing");
+    expect(res.status).toBe(200);
+    expect(res.text).toContain("Key Already Provisioned");
+  });
+
+  it("provisions new key on success", async () => {
+    mockStripe.checkout.sessions.retrieve.mockResolvedValue({
+      id: "cs_new",
+      customer: "cus_new",
+      customer_details: { email: "new@test.com" },
+    });
+    const { createProKey } = await import("../services/keys.js");
+    const res = await request(app).get("/v1/billing/success?session_id=cs_new");
+    expect(res.status).toBe(200);
+    expect(res.text).toContain("Welcome to Pro");
+    expect(createProKey).toHaveBeenCalledWith("new@test.com", "cus_new");
+  });
+
+  it("returns 500 on Stripe error", async () => {
+    mockStripe.checkout.sessions.retrieve.mockRejectedValue(new Error("Stripe error"));
+    const res = await request(app).get("/v1/billing/success?session_id=cs_err");
+    expect(res.status).toBe(500);
+  });
+});
+
+describe("POST /v1/billing/webhook", () => {
+  it("returns 500 when webhook secret missing", async () => {
+    delete process.env.STRIPE_WEBHOOK_SECRET;
+    // Need to re-import to pick up env change - but the router is already loaded
+    // The router reads env at request time, so this should work
+    const savedSecret = process.env.STRIPE_WEBHOOK_SECRET;
+    process.env.STRIPE_WEBHOOK_SECRET = "";
+    delete process.env.STRIPE_WEBHOOK_SECRET;
+
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "sig_test")
+      .send(JSON.stringify({ type: "test" }));
+    expect(res.status).toBe(500);
+
+    process.env.STRIPE_WEBHOOK_SECRET = "whsec_test_fake";
+  });
+
+  it("returns 400 for missing signature", async () => {
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .send(JSON.stringify({ type: "test" }));
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/Missing stripe-signature/);
+  });
+
+  it("returns 400 for invalid signature", async () => {
+    mockStripe.webhooks.constructEvent.mockImplementation(() => {
+      throw new Error("Invalid signature");
+    });
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "bad_sig")
+      .send(JSON.stringify({ type: "test" }));
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/Invalid signature/);
+  });
+
+  it("provisions key on checkout.session.completed for DocFast product", async () => {
+    mockStripe.webhooks.constructEvent.mockReturnValue({
+      type: "checkout.session.completed",
+      data: {
+        object: {
+          id: "cs_wh",
+          customer: "cus_wh",
+          customer_details: { email: "wh@test.com" },
+        },
+      },
+    });
+    mockStripe.checkout.sessions.retrieve.mockResolvedValue({
+      id: "cs_wh",
+      line_items: {
+        data: [{ price: { product: "prod_TygeG8tQPtEAdE" } }],
+      },
+    });
+    const { createProKey } = await import("../services/keys.js");
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "valid_sig")
+      .send(JSON.stringify({ type: "checkout.session.completed" }));
+    expect(res.status).toBe(200);
+    expect(res.body.received).toBe(true);
+    expect(createProKey).toHaveBeenCalledWith("wh@test.com", "cus_wh");
+  });
+
+  it("ignores checkout.session.completed for non-DocFast product", async () => {
+    mockStripe.webhooks.constructEvent.mockReturnValue({
+      type: "checkout.session.completed",
+      data: {
+        object: {
+          id: "cs_other",
+          customer: "cus_other",
+          customer_details: { email: "other@test.com" },
+        },
+      },
+    });
+    mockStripe.checkout.sessions.retrieve.mockResolvedValue({
+      id: "cs_other",
+      line_items: {
+        data: [{ price: { product: "prod_OTHER" } }],
+      },
+    });
+    const { createProKey } = await import("../services/keys.js");
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "valid_sig")
+      .send(JSON.stringify({ type: "checkout.session.completed" }));
+    expect(res.status).toBe(200);
+    expect(createProKey).not.toHaveBeenCalled();
+  });
+
+  it("downgrades on customer.subscription.deleted", async () => {
+    mockStripe.webhooks.constructEvent.mockReturnValue({
+      type: "customer.subscription.deleted",
+      data: {
+        object: { id: "sub_del", customer: "cus_del" },
+      },
+    });
+    mockStripe.subscriptions.retrieve.mockResolvedValue({
+      items: { data: [{ price: { product: { id: "prod_TygeG8tQPtEAdE" } } }] },
+    });
+    const { downgradeByCustomer } = await import("../services/keys.js");
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "valid_sig")
+      .send(JSON.stringify({ type: "customer.subscription.deleted" }));
+    expect(res.status).toBe(200);
+    expect(downgradeByCustomer).toHaveBeenCalledWith("cus_del");
+  });
+
+  it("downgrades on customer.subscription.updated with cancel_at_period_end", async () => {
+    mockStripe.webhooks.constructEvent.mockReturnValue({
+      type: "customer.subscription.updated",
+      data: {
+        object: { id: "sub_cancel", customer: "cus_cancel", status: "active", cancel_at_period_end: true },
+      },
+    });
+    mockStripe.subscriptions.retrieve.mockResolvedValue({
+      items: { data: [{ price: { product: { id: "prod_TygeG8tQPtEAdE" } } }] },
+    });
+    const { downgradeByCustomer } = await import("../services/keys.js");
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "valid_sig")
+      .send(JSON.stringify({ type: "customer.subscription.updated" }));
+    expect(res.status).toBe(200);
+    expect(downgradeByCustomer).toHaveBeenCalledWith("cus_cancel");
+  });
+
+  it("syncs email on customer.updated", async () => {
+    mockStripe.webhooks.constructEvent.mockReturnValue({
+      type: "customer.updated",
+      data: {
+        object: { id: "cus_email", email: "newemail@test.com" },
+      },
+    });
+    const { updateEmailByCustomer } = await import("../services/keys.js");
+    const res = await request(app)
+      .post("/v1/billing/webhook")
+      .set("content-type", "application/json")
+      .set("stripe-signature", "valid_sig")
+      .send(JSON.stringify({ type: "customer.updated" }));
+    expect(res.status).toBe(200);
+    expect(updateEmailByCustomer).toHaveBeenCalledWith("cus_email", "newemail@test.com");
+  });
+});
diff --git a/src/__tests__/convert.test.ts b/src/__tests__/convert.test.ts
new file mode 100644
index 0000000..5cc7c1c
--- /dev/null
+++ b/src/__tests__/convert.test.ts
@@ -0,0 +1,184 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import express from "express";
+import request from "supertest";
+
+// Mock dns before imports
+vi.mock("node:dns/promises", () => ({
+  default: { lookup: vi.fn() },
+  lookup: vi.fn(),
+}));
+
+let app: express.Express;
+
+beforeEach(async () => {
+  vi.clearAllMocks();
+  vi.resetModules();
+
+  const { renderPdf, renderUrlPdf } = await import("../services/browser.js");
+  vi.mocked(renderPdf).mockResolvedValue(Buffer.from("%PDF-1.4 mock"));
+  vi.mocked(renderUrlPdf).mockResolvedValue(Buffer.from("%PDF-1.4 mock url"));
+
+  const dns = await import("node:dns/promises");
+  vi.mocked(dns.default.lookup).mockResolvedValue({ address: "93.184.216.34", family: 4 } as any);
+
+  const { convertRouter } = await import("../routes/convert.js");
+  app = express();
+  app.use(express.json({ limit: "500kb" }));
+  app.use("/v1/convert", convertRouter);
+});
+
+describe("POST /v1/convert/html", () => {
+  it("returns 400 for missing html", async () => {
+    const res = await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "application/json")
+      .send({});
+    expect(res.status).toBe(400);
+  });
+
+  it("returns 415 for wrong content-type", async () => {
+    const res = await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "text/plain")
+      .send("html=<h1>hi</h1>");
+    expect(res.status).toBe(415);
+  });
+
+  it("returns PDF on success", async () => {
+    const res = await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "application/json")
+      .send({ html: "<h1>Hello</h1>" });
+    expect(res.status).toBe(200);
+    expect(res.headers["content-type"]).toMatch(/application\/pdf/);
+  });
+
+  it("returns 429 on QUEUE_FULL", async () => {
+    const { renderPdf } = await import("../services/browser.js");
+    vi.mocked(renderPdf).mockRejectedValue(new Error("QUEUE_FULL"));
+    const res = await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "application/json")
+      .send({ html: "<h1>Hello</h1>" });
+    expect(res.status).toBe(429);
+  });
+
+  it("returns 500 on PDF_TIMEOUT", async () => {
+    const { renderPdf } = await import("../services/browser.js");
+    vi.mocked(renderPdf).mockRejectedValue(new Error("PDF_TIMEOUT"));
+    const res = await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "application/json")
+      .send({ html: "<h1>Hello</h1>" });
+    expect(res.status).toBe(500);
+    expect(res.body.error).toMatch(/PDF_TIMEOUT/);
+  });
+
+  it("wraps fragments (no <html tag) with wrapHtml", async () => {
+    const { renderPdf } = await import("../services/browser.js");
+    await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "application/json")
+      .send({ html: "<h1>Fragment</h1>" });
+    // wrapHtml should have been called; renderPdf receives wrapped HTML
+    const calledHtml = vi.mocked(renderPdf).mock.calls[0][0];
+    expect(calledHtml).toContain("<html");
+  });
+
+  it("passes full HTML documents as-is", async () => {
+    const { renderPdf } = await import("../services/browser.js");
+    const fullDoc = "<html><body><h1>Full</h1></body></html>";
+    await request(app)
+      .post("/v1/convert/html")
+      .set("content-type", "application/json")
+      .send({ html: fullDoc });
+    const calledHtml = vi.mocked(renderPdf).mock.calls[0][0];
+    expect(calledHtml).toBe(fullDoc);
+  });
+});
+
+describe("POST /v1/convert/markdown", () => {
+  it("returns 400 for missing markdown", async () => {
+    const res = await request(app)
+      .post("/v1/convert/markdown")
+      .set("content-type", "application/json")
+      .send({});
+    expect(res.status).toBe(400);
+  });
+
+  it("returns 415 for wrong content-type", async () => {
+    const res = await request(app)
+      .post("/v1/convert/markdown")
+      .set("content-type", "text/plain")
+      .send("markdown=# hi");
+    expect(res.status).toBe(415);
+  });
+
+  it("returns PDF on success", async () => {
+    const res = await request(app)
+      .post("/v1/convert/markdown")
+      .set("content-type", "application/json")
+      .send({ markdown: "# Hello World" });
+    expect(res.status).toBe(200);
+    expect(res.headers["content-type"]).toMatch(/application\/pdf/);
+  });
+});
+
+describe("POST /v1/convert/url", () => {
+  it("returns 400 for missing url", async () => {
+    const res = await request(app)
+      .post("/v1/convert/url")
+      .set("content-type", "application/json")
+      .send({});
+    expect(res.status).toBe(400);
+  });
+
+  it("returns 400 for invalid URL", async () => {
+    const res = await request(app)
+      .post("/v1/convert/url")
+      .set("content-type", "application/json")
+      .send({ url: "not a url" });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/Invalid URL/);
+  });
+
+  it("returns 400 for non-http protocol", async () => {
+    const res = await request(app)
+      .post("/v1/convert/url")
+      .set("content-type", "application/json")
+      .send({ url: "ftp://example.com" });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/http\/https/);
+  });
+
+  it("returns 400 for private IP", async () => {
+    const dns = await import("node:dns/promises");
+    vi.mocked(dns.default.lookup).mockResolvedValue({ address: "192.168.1.1", family: 4 } as any);
+    const res = await request(app)
+      .post("/v1/convert/url")
+      .set("content-type", "application/json")
+      .send({ url: "https://internal.example.com" });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/private/i);
+  });
+
+  it("returns 400 for DNS failure", async () => {
+    const dns = await import("node:dns/promises");
+    vi.mocked(dns.default.lookup).mockRejectedValue(new Error("ENOTFOUND"));
+    const res = await request(app)
+      .post("/v1/convert/url")
+      .set("content-type", "application/json")
+      .send({ url: "https://nonexistent.example.com" });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/DNS/);
+  });
+
+  it("returns PDF on success", async () => {
+    const res = await request(app)
+      .post("/v1/convert/url")
+      .set("content-type", "application/json")
+      .send({ url: "https://example.com" });
+    expect(res.status).toBe(200);
+    expect(res.headers["content-type"]).toMatch(/application\/pdf/);
+  });
+});